In the prior art, slip rings, roll rings, mercury contact assemblies, and other devices have been used to transmit electrical power or data signals across a rotating mechanical interface. Related technology includes brushes in many types of motors and torque sensors.
Slip rings, which use ring and brush contact to transmit electricity across a rotating interface, have problems in that they wear quickly (due to sliding friction of brushes), carry only one channel per layer of brushes, can be electrically noisy, induce too much torque resistance, and generate particle debris through wear. Debris is not a desirable quality for many clean room and aerospace applications. Slip rings are also difficult to align and relatively costly, and have no use in the transfer of mechanical power.
Roll rings have limitations in that only one ring can be used per layer of assembly for signal transfer. Roll rings also present alignment difficulties in assembly and do not possess suitable mechanical power transmission potential. Mercury contact assemblies are not compact, possess no mechanical power transfer potential, can be costly, and are associated with hazardous material (outgassing of mercury vapor).